Method of and apparatus fob burn



Oct. 26, 1937. A. P. SAHA METHOD OF AND APPARATUS FOR BURNING FLUID FUEL Filed March 15, 1935 INVENTOR fizz/i0 Ja/m I1 ATTORNEYS Patented Oct. 26, 1937 UNITED STATES PATENT OFFICE METHOD OF AND APPARATUS FOR BURN- ING FLUID FUEL 8 Claims.

The present invention relates to a method and apparatus for effecting the combustion of fluid fuels, 1. e. gaseous or liquid fuels.

More particularly the invention relates to a novel and improved method and apparatus for effecting diffusion combustion of gases and liquid fuels or 0t er fuels which maybe converted into a gaseo 'or vaporized state prior to combustion.

An object of my invention is to provide an im- Proved method of combustion in which substantially complete and perfect combustion may be obtained and which has special utility in the flring of heat transmission apparatus, furnaces and any other apparatus where the object is the transformation of the potential energy of fuel into useful heat. It is also an object of my invention to produce an apparatus which may be used in carrying out this method.

Another object of my invention is the provision of a method and apparatus by which a high rate of heat emission is effected, or in other words,

. a method and apparatus in which an increased transfer of heat, by radiation from the flame, is effected.

A further object of my invention is to provide a method and apparatus in which the rate of combustion may be varied over large ranges.

Other objects are to provide an apparatus of simple, practical construction, dependable in operation, durable in use, and capable of effecting substantial fuel economy due to efficiency in operation and to provide an apparatus of this character which is of a compact, inexpensive 35 construction.

Further objects of my invention will be apparent from a consideration of the description herein, especially when considered in connection with the accompanying drawing forming a part of the specification and in which:

combustion apparatus embodying the invention 0 but having modified forms of the fuel and air intakes; I

Fig. 4 is a view in transverse section taken on the line IV-IV of Fig. 3 looking in the direction of the arrows.

Fig. 5 is a view in transverse section talgen on the line VV of Fig. 3, looking in the direction of the arrows.

Fig. 6 is a fragmentary view in vertical section of a vertical boiler with which the improved combustion apparatus is associated and shows another form of fuel intake.

Fig. '7 is a view in vertical section of a horizontal boiler with which the improved combustion apparatus. is associated and shows still another form of fuel intake.

In the combustion of gaseous fuels the characteristics of the flame produced may be controlled largely by the manner and rate of mixing the fuel gas and the air prior to the actual combustion, and by the manner and rate of combustion turbulence, or the oxygen concentration with reference to the fuel, during the process of combustion.

If a high rate of combustion is desired it may be obtained by pre-mixing with a gaseous fuel a part or all of the air required for the combustion previous to the burning, and also by causing a turbulence in the air and fuel gas during the combustion. In the case of turbulent combustion of this type, the combustion reactions are based on the hydroxylation theory. According to this theory the hydrocarbons combine with oxygen to form intermediate hydroxylated products such as alcohols and aldehydes; these intermediate products are then oxydized to the final products of carbon dioxide and water. The turbulence causes the combustion supporting air to be intimately associated with the fuel gas and therefore causes the hydroxylation reactions to take place, resulting in a more or less short, non-luminous flame. Even though a high rate of combustion and a high degree of heat liberation may be effected, the heat transference to any object will be obtained primarily by convection and to some degree by radiation from the hot gases and therefore comparatively slowly.

If a slow or delayed combustion is desired the fuel gas and the combustion supporting air are not pre-mixed, but rather the fuel gas and the air meet coincidentally with the occurrence of combustion. The combustion may bejurther delayed by decreasing the turbulence and by eliminating to a great extent the mixing .of the air and fuel gas during combustion. When. the fuelgas and air contact in this manner the resulting combustion occurs through molecular inter-diffusion. Combustion of this type is not only slower, but produces a luminous flame. Combustion producing a luminous flame is represented by a different set of chemical reactions. The principal gases and by convection.

As has been mentioned, the heat transference in the case of a non-luminous flame is primarily limited to heat radiated from the hot gases and to heat transferred by convection, and for this reason it has been realized for some time that radiation from luminous flames plays an important part in heat transfer problems. Heretofore, when fuel is burned in an ordinary luminous flame, the flame temperature is reduced because of the incomplete combustion of the carbon particles. The gain of heat transmission due to increased emissivity is then to some extent counteracted by the reduction in flame temperature due to the inability to burn the carbon particles completely. Consequently, in the past, attempts to use luminous flames as a means of increasing the heat transfer have not resulted successfully.

According to the present invention, the flows of the combustion supporting air and of the fuel in gaseous or vaporous state are such as to insure the maintenance of constant conditions in thecombustion space. The combustion supporting air and the fuel gases-always maintain the same relative positions within the combustion chamber.

Consequently, the combustion progresses at a constant rate throughout the combustion chamber. and the thermal break-down of the hydrocarbons to form luminous carbon particles is uniform. This results in practically a constant rate of radiation for the entire combustion space. It also insures a constant radiation emissivity, and therefore a constant flame temperature for the entire combustion space results.

In carrying out the method of this invention the gaseous fuel is introduced. into the center of the combustion chamber, and subjected to a thermal break-down into carbonparticles which then became heated to incandescence by the heat of the flame. Combustion of the particles takes place' as they contact a surrounding atmosphere of combustion supporting air which is ample in quantity and so distributed as to cause a complete combustion of the carbon particles. As a result of complete combustion, the flame is maintained at a maximum temperature and a high degree of heat transmission through radiation results.

In order to accomplish this the combustion supporting air is caused to flow into and through a combustion chamber in substantially the form of a free spiral vortex. A free spiral vortex has an annular cross section and the air constituting this portion of the vortex moves through the combustion chamber with tangential and axial velocity components. If the combustion chamber is diverging or converging the air will also move with a radial velocity component. As a result, the airmoves in spiral paths. The tangential velocity component of the air varies inversely as the distance from the axis of the core so that the vortex is, in effect, composed of a number of concentric strata which possess a progressively different tangential velocity. The air of the vortex also hasan axial velocity. The strata farther from the axis of the core will move axially through the combustion chamber with a higher axial velocity component than the strata nearer the axis of the core.

' By free vortex is meant any rotating body of fluid in which the tangential velocity component varies inversely as the distance from the axis of rotation. Further discussion of vortices, which support this defintion may be found in "Hydraulics by A. H. Gibson, page 103, published by Van Nostrand, 1925, and A. S. M. E. Transactions, 1921, paper 1824; Present Trend of Turbine Development" by L. F. Moody. A moving fluid may also have an axial or radial velocity component, or both, in addition to the tangential component. By a free spiral vortex is meant that species of a free vortex in which the motion is compounded of two or three of these motions in any proportions so long as the tangential velocity component varies inversely as the distance from the axis. See W. J. M. Rankine: A Manual of Applied Mechanics (16th Ed.) p. 576, published by Chas. Griflin & Co., London (1901).

Along the axis of the free spiral vortex a core is formed. In the core the fluid has substantially only a tangential velocity and this varies as the distance from the center of the core. It will be seen, therefore, that the inner layer of the combustion supporting air and the outer layer of the core have substantially identical motion. The free spiral vortex, therefore, may serve as the combustion supporting space while the core functions as the fuel delivering space.

Referring more particularly to the process and apparatus shown in the drawing, the method of combustion is carried out in a combustion chamber or furnace which may be considered as a passage for combustion supporting air, fuel and products of combustion. In Figs. 1, 6, and 7, the combustion chamber is shown incorporated in a boiler, the water level being indicated at I. It is to be understood, however, that the method may be carried out with reference to any apparatus used in heating. The walls 2 of the combustion chamber are preferably surfaces of revolution but other forms, for example, polygonal in cross section, may be used. The walls may be composed of metal or refractory material. The combustion chamber is usually cylindrical in form, but it may be conical with diverging or converging walls. Any variation in the cross section of the chamber is permissible if such variation is gradual so that sudden changes in the flow of the fluid are avoided.

The combustion supporting air is introduced into.the combustion chamber by a device generally indicated at A and moves therethrough in substantially the form of a free spiral vortex 3 inside of which is a core 4, substantially free from flow of combustion supporting air. The vortex may be formed with a core of any desired diameter depending upon the combustion conditions desired.

The fuel is introduced into the core by a device generally indicated at B and is ignited in a conventional manner, for example, through the opening H. The fuel within the core becomes heated so that it is subjected to a thermal breakdown, yielding particles of free carbon which are heated to incandescence. The particles within the core do not burn to any material extent, sincethe necessary air within the core is lacking. As the particles move around within the core they come in contact with the innermost strata of the air of the vortex and are burned very rapidly. The hot products of combustion diffuse into the air stream and are eliminated from the combustion chamber as the vortex exits therefrom.

Some of the hot products of combustion will break-down of the hydrocarbons into hydrogen and carbon particles. The hydrogen and the carbon particles contact the air stream as. explained above and are burned.

Since the contacting surfaces of the air stream and of the core have substantially identical motion there is little or no relative movement between the air and the fuel streams at their boundary. When the absolute velocity of the air of the vortex is below the critical velocity, the admixture of air and fuel will take place primarily by molecular interdiffusion. When the absolute velocity of the air of the vortex exceeds the critical velocity, a turbulent flow exists in the annular air stream. However, this has no effect on the tangential and axial velocity components of the air in the vortex, and does not alter the relatively separate flow conditions of the air and fuel streams; Since a turbulent flow will exist in the air stream, the admixture of the air and fuel will be accelerated.

Various devices may be used for forming the vortex and two such devices are shown in the drawing as illustrative. In Figs. 1 and 2 is shown a spiral casing 6 which imparts the vortical movement to the air as it enters through the opening 1 under pressure. An adjustable vane 8 may be located at different positions in order to vary the diameter of the vortex core. In Figs. 3 and 5 is shown another modification in which tangentially arranged guide vanes 8a impart the vortical movement to the air as t enters under pressure through the opening I. The vanes may be pivoted as at 9 and placed in different angular positions to alter the diameter of the core of the vortex. Other devices may be .used to impart a vortical movement to the air and the invention is not to be understood as limited to the specific mechanical construction here shown for illustrative purposes.

Alteration of the pressure of the air being introduced'through the opening I will not alter the diameter of the core. Increase in pressure will increase the absolute velocity of the air particles moving in the vortex and, therefore, cause more air to pass through the combustion chamber. When the core is of relatively large diameter the mean tangential velocity component of the air in the vortex will be high as compared with the mean axial component. When the core is relatively small the mean axial component of the velocity will be relatively high as compared with the mean tangential component. For a constant pressure of air in the opening I a decrease in the size of the core will increase the mean axial velocity component and, therefore, increase the amount of air passing through the chamber. It will, therefore, be seen that the quantity of air passing through the combustion chamber may be regulated by altering the position of the vanes, or by varying the pressure, or by a combination of both.

Various devices may be used for introducing the fuel into the core of the vortex and several such devices are shown in the drawing as illustrative.

If a liquid fuel is to be burned it is introduced in a finely divided state. This may be effected by an atomizer l3 employing air, steam or fuel gas as the atomizing medium, or by a mechanical atomizer. The atomized particles of liquid are vaporized within the core by the heat of 'commanner as though a gas had been introduced. If it is desired, the liquid fuel may be vaporized before it is introduced into the core. In Fig. 6 is shown a modification in which the liquid fuel contacts a heated member ID and the vapor arising therefrom passes into the core. It may also be vaporized by any other means. Y

If a gaseous fuel is being utilized it may be introduced through a single orifice such as shown at II in Fig. 'l or'through a plurality of orifices such as illustrated at I! in Figs. 3 and 4. In this last modification the inlets are so arranged as to impart a whirling movement to the gas.

Any other device may be used for introducing the liquid or gaseous fuel into the core or vortex. My invention is not to be interpreted as limited to any of the specific constructions here shown as illustrative.

Any of the fuel intake devices may be used in combination with any of the air intake devices as desired.

The products-of combustion exit at the other end of the combustion chamber. The combustion chamber may be simply left open at this end or may have associated therewith a spiral casing C (Fig. 1) similar to the construction of the casing at the other end and through which the products of combustion exit. A device may be employed whereby the products exit radially.

vof time being constant), the type of combustion and. the characteristics of the resulting flame may be varied by varying the absolute velocity of the combustion supporting air. If the absolute velocity is to be increased it may be accomplished, for example, by increasing the pressure of the air entering the furnace and increasing the diameter of the core of the vortex. The greater the absolute velocity of the air the greater will be the rate at which the fuel and air contact, because of the increased turbulence in the annular air stream. The rate at which the fuel particles are burned is proportional to the rate at which oxygen is supplied to them. In other words, the increase of absolute velocity of combustion supporting air results in an increased rate of heat release per unit volume of combustion space. The higher the heat release per unit volume of combustion space, the shorter will be the flame. Because, there is sufficient oxygenfor hydroxylation of a portion of the fuel, the amount of thermal breakdown of the fuel will be reduced. The increased rate of heat release, therefore, results in decreased emissivity evidenced by decreased luminosity of the flame.

Alternatively, if it is desired, a certain amount of air may be pre-mixed with fuel before being introduced into the core. A portion of the fuel, therefore, will burn by the hydroxylation process and the rate of heat release or speed of combusticn will be increased.

Conversely, with a given furnace and a given heat load (quantity of fuel and air consumed per unit of time beng constant) the emitted radiation may be increased by decreasing the absolute velocity of the combustion supporting air. This decreases the turbulence in the annular vortex of air and consequently the rate at which the air contacts the fuel. Therefore, a greater time. interval is secured between the thermal break-down of the fuel and the subsequent oxidation of the resulting carbon particles. In general the emitted radiation increases with the increase of the flame thickness according to an exponential law and the intensity of emission for any given thickness increases with the concentration of incandescent carbon particles in it. Flames may be generated having a maximum concentration of incandescent solid material. The intensity of emission of such flames closely approach black body value.

The method of combustion may be advantageously employed in connection with combustion chambers or funaces in which the heat load varies. When the load is high a larger quantity of fuel is necessarily consumed and a larger quantity of air must pass through the combustion chamber to support the increased combustion. The amount of air passing through the vortex can be varied by altering the diameter of the core. For example, with a high heat load, a

smaller core is used in which case the mean axial velocity component of theair is greater and a larger quantity of air passes through the combustion chamber.

The expression fluid is used herein in its generic sense to refer to a material in either a liquid or gaseous state.

In my application Serial No. 676,780, filed June 21, 1933, I have disclosed a method and apparatus employing a free spiral vortex in effecting combustion. In that case fuel particles, either liquid or solid, are burned while in suspension; due to the fact that the particles are of sufficient size to respond to the effects of centrifugal force they move radially through concentric air currents and hence a different method of combustion results than that described here. In this application the fuel is in gaseous form before combustion begins and hence burns by interdiifusion with the combustion supporting air.

Various modifications of my invention will be apparent to those skilled in the art and while I have not illustrated my invention with every variation of the method and apparatus that may be employed within its scope, I intend my invention to include all such modifications as may be embraced within the following claims.

I claim:

1. An apparatus for burning fluid fuel by diffusion comprising in combination a combustion chamber having an' interior surface of a transverse cross sectional shape to maintain substantially a free spiral vortex therein and having an air inlet at one end thereof, means at the air inlet end of said combustion chamber for introducing air in the form of a free spiral vortex into the combustion chamber, the proportions of the combustion chamber in respect to said means for producing the vortex being such that the air is maintained in substantially a free spiral vortex within the combustion chamber, and means for introducing the fluid fuel into said vortex.

2. An apparatus for burning gaseous fuel by diffusion comprising in combination a combustion chamber having an interior surface of a transverse cross sectional shape to maintain substantially a free spiral vortex therein and having an air inlet at one end thereof, means at the air inlet end of said combustion chamber for introducing air in the form of a free spiral vortex into the combustion chamber, the proportions of the combustion chamber in respect to said means for producing the vortex being such that the air is maintained in substantially a free spiral vortex within the combustion chamber, and means for introducing the gaseous fuel into said vortex.

3. An apparatus for burninsliquid fuel by diffusion comprising in combination a combustion chamber having an interior surface of a transverse cross sectional shape to maintain substantially a free spiral vortex therein and having an air inlet at one end thereof, means at the air inlet end of said combustion chamber for introducingair in the form of a free spiral vortex into the combustion chamber, the proportions of the combustion chamber in respect to said means for producing the vortex being such that the air is maintained in substantially a free spiral vortex within the combustion chamber, and means for introducing the liquid fuel into said vortex.

4. An apparatus for burning gaseous fuel by diffusion comprisingin combination a substantially cylindrical combustion chamber having an air inlet, at one end thereof, means at the air inlet end of the combustion chamber for introducing air in the form of a free spiral vortex into the combustion chamber, the proportions of the combustion chamber in respect to said means for producing the vortex being such that the air is maintained in substantially a free spiral vortex. within the combustion chamber, and means at said end of the combustion chamber for introducing the gaseous fuel into said vortex.

5. An apparatus for burning fluid fuel by diffusion comprising in combination a combustion chamber having an interior surface of a transverse cross sectional shape to maintain substantially a free spiral vortex therein and having an air inlet at one end thereof, means at the air inlet end of the combustion chamber for introducing air in the form of a free spiral vortex into the combustion chamber, the. proportions of the combustion chamber in respect to said means for producing the vortex being such that the air is maintained in substantially a free spiral vortex within the combustion chamber, said means including an element movable to alter the diameter of the core of said vortex, and means at said end of the combustion chamber for introducing the fluid fuel into said vortex.

6. A method for effecting diffusion combustion of a fluid fuel, which comprises forming and maintaining substantially a free spiral vortex of combustion supporting air, and introducing the fluid fuel into the core of the vortex while combustion is proceeding as the result of an initial ignition, said combustion maintaining a temperature such as to ignite said fuel at the common boundary of the core and the combustion supporting air, whereby burning continues as the fuel diffuses through the surrounding vortical stream of combustion supporting air.

7. A method of effecting diffusion combustion of a gaseous fuel which comprises forming and maintaining substantially a free spiral vortex of combustion supporting air, and introducing the gaseous fuel into the core of said vortex while combustion is proceeding as the result of an initial ignition, said combustion maintaining a temperature such as to ignite said'fuel at the common boundary of the core and the combustion supporting air, whereby burning continues as the fuel diffuses through the surrounding vortical stream of combustion supporting air.

8. A method of efi'ecting diffusion combustion of a liquid fuel, which comprises forming and maintaining substantially a free spiral vortex of combustion supporting air, and introducing the liquid fuel into the core of said vortex in atomized condition while combustion is proceeding as the result of an initial ignition, the combustion maintaining a temperature such as to vaporize the fuel and ignite it at the common boundary of the core and the combustion supporting air, whereby burning continues as the vaporized fuel difiuses through the surrounding vortical stream of combustion supporting air.

AA'I'I'O P. SAHA. 

